In recent years, from social demands for low-fuel consumption and low exhaust emission, there has been an increased attention to an electric vehicle or a hybrid vehicle equipped with an alternate-current (AC) motor to run. For example, in a hybrid vehicle, an AC motor is connected to a direct-current (DC) power source such as a rechargeable battery unit through a power converter such as an inverter. The inverter converts a DC voltage supplied from the DC power source to an AC voltage and drives the AC motor with the AC voltage.
JP-A-2008-86139 corresponding to US 2008/0079385 discloses a one-phase control technique for reducing the number of current sensors used in a control apparatus for an AC motor mounted on an electric vehicle or a hybrid vehicle, thereby reducing the size of the apparatus near output terminals of the inverter and the cost of a control system of the AC motor. In the one-phase control technique, a current sensor for detecting a phase current is provided to only one phase of the AC motor.